Replacement of a shared, high resolution transmission electron microscope in the Molecular Biology Institute at UCLA is requested. The existing, shared 10-year old EM has had repeated failures and breakdowns resulting in lost research time to at least 6 research groups. No other instruments are available within the building or in other departments on a regular basis, for work on the structure and intracellular localization of macromolecules. The instrument requested will be used primarily by the research groups of Drs. D. Eisenberg, F. Eiserling, J. Fessler and V. Schumaker. Dr. Eiserling is the director of the shared EM facility and has overall responsibility for its management, while a full-time technician, Barbara Mueller, is responsible for daily maintenance and instruction. An advisory committee consisting of Drs. Eiserling, Fessler and Schumaker are responsible for setting policy regarding the instrument. New users are trained as needed, and in a biannual course in structural molecular biology taught by Dr. Eiserling and Ms. Mueller. The instrument will be used for ongoing projects supported by NIH grants: Dr. Eisenberg works on the three-dimensional arrangements of multisubunit enzymes; Dr. Eiserling studies the regulation of shape and size of virus components; Dr. Fessler examines the structure of connective tissue macromolecules and Dr. Schumaker elucidates the structural relationships of the components of complement and lipoproteins. All these projects require extensive use of high resolution electron microscopy that will be made available with a new, reliable instrument.